Peripheral hypercapnic chemosensitivity at rest and progressive exercise intensities in males and females

Abstract

Peripheral hypercapnic chemosensitivity (PHC) is the ventilatory response to hypercapnia and is enhanced with acute whole body exercise. However, little is known about the mechanism(s) responsible for the exercise-related increase in PHC and if progressive exercise leads to further augmentation. We hypothesized that unloaded cycle exercise (0 W) would increase PHC but progressively increasing the intensity would not further augment the response. Twenty healthy subjects completed two testing days. Day 1 was a maximal exercise test on a cycle ergometer to determine peak power output (W_max). Day 2 consisted of six 12-min stages: 1) rest on chair, 2) rest on bike, 3) 0 W unloaded cycling, 4) 25% W_max, 5) 50% W_max, and 6) ∼70% W_max with ∼10 min of rest between each exercise stage. In each stage, PHC was assessed via two breaths of 10% CO_{2 (∼21% O2)} repeated five times with ∼45 s between each to ensure end-tidal CO₂ ([Formula: see text]) and ventilation returned to baseline. Prestimulus [Formula: see text] was not different between rest and unloaded cycling (P = 0.478). There was a significant increase in PHC between seated rest and 25% W_max (0.71 ± 0.37 vs. 1.03 ± 0.52 L·mmHg^-1·min^-1, respectively, P = 0.0006) and between seated rest and unloaded cycling (0.71 ± 0.37 vs. 1.04 ± 0.4 L·mmHg^-1·min^-1, respectively, P = 0.0017). There was no effect of exercise intensity on PHC (1.03 ± 0.52 vs. 0.95 ± 0.58 vs. 1.01 ± 0.65 L·mmHg^-1·min^-1 for 25, 50, and 70% W_max, P = 0.44). The increased PHC response from seated rest to unloaded and 25% W_max, but no effect of exercise intensity suggests a possible feedforward/feedback mechanism causing increased PHC sensitivity through the act of cycling.NEW & NOTEWORTHY Unloaded exercise significantly increased the peripheral hypercapnic ventilatory response (HCVR) compared with rest. However, increases in exercise intensity did not further augment peripheral HCVR. Males had a greater peripheral HCVR compared with females, but there was no interaction between sex and intensity. The lack of sex interactions suggests the mechanism augmenting the peripheral HCVR with exercise is independent of sex. The increase in peripheral HCVR with exercise is likely due to central command.

Keywords: carbon dioxide; central command; control of hyperpnea; ventilation.